Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0029463 (osteosarcoma)
 16,637 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An osteoblast calcium channel demonstrated by single channel recordings is associated with calcium antagonist receptor binding sites in osteoblast-like osteosarcoma cells. By using whole cell current recordings we now show that this channel is stimulated by the dihydropyridine calcium agonist drug BAY K 8644. A physiological relevance of these channels is apparent from the stereoselective, potent inhibition of parathyroid hormone-stimulated calcium uptake into osteoblast-like cells in culture by desmethoxyverapamil, a phenylalkylamine calcium antagonist. Secretion by these cells of the bone matrix protein osteocalcin is stimulated by BAY K 8644 and blocked by desmethoxyverapamil and nitrendipine. Evidence for a role of this channel in bone remodeling in intact animals comes from enhanced bone resorption in fetal rat bones observed with BAY K 8644 and stereoselective, potent blockade of resorption by desmethoxyverapamil.
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PMID:Bone remodeling signaled by a dihydropyridine- and phenylalkylamine-sensitive calcium channel. 246 65

Whole cell patch clamp studies on osteoblast-like rat osteosarcoma cells (ROS 17/2.8) show the existence of L-type calcium channels in the cell membrane. Measurements were carried out at both 21 and 37 degrees C. With isotonic CsCl in the pipette and a bathing medium containing either 110 or 10 mM Ba2+, a strong depolarizing pulse was required to activate an inward current. The current-voltage relationship (I-V) of this inward current showed a maximum amplitude near +30 mV at 21 and 37 degrees C, with 110 mM Ba2+ in the bathing medium, and near +10 mV at 37 degrees C with 10 mM Ba2+. At both 21 and 37 degrees C the dihydropyridine, BAY K 8644 (2 microM), increased this current and shifted the I-V maximum to less positive potentials, while nifedipine (5 microM) reduced the current. Cd2+ (50 microM) and Co2+ (100 microM) blocked the current. At 21 degrees C the measured inward current showed a slow inactivation, with a time constant of some hundreds of milliseconds. At 37 degrees C, inactivation was considerably faster. The current was suppressed by holding the membrane potential more positive than -30 mV. These data are strong evidence that ROS 17/2.8 cells have a significant number of 'L-type' calcium channels.
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PMID:Osteoblastic cells have L-type calcium channels. 247 37

A slowly inactivating inward calcium current was identified in the rat osteosarcoma cell line ROS 17/2.8 using a combination of ion flux and electrophysiological techniques. Voltage dependence, dihydropyridine sensitivity, divalent cation selectivity, and single channel properties identified this current as a high threshold, "L-type" calcium current. Ion flux experiments using 45Ca2+ confirmed that calcium uptake through these channel represents a major pathway for calcium entry into osteosarcoma cells. In resting cells, i.e. at negative membrane potentials, stimulation of both calcium current and rapid 45Ca2+ influx could be elicited by concentrations of 1,25-(OH)2-vitamin D3 between 0.1 and 3 nM. At these concentrations, 1,25-(OH)2-vitamin D3 shifted the threshold for activation of inward calcium current to more negative potentials. At higher concentrations (5-10 nM), inhibitory effects became predominant. These opposing effects are functionally similar to those of the dihydropyridine BAY K 8644. Other vitamin D3 metabolites (25-(OH)-D3 and 24,25-(OH)2-D3) exhibited less potent stimulatory effects and greater inhibition of calcium current than 1,25-(OH)2-D3. These results suggest that (i) vitamin D3 acts as a potent modulator of calcium channel function in osteosarcoma cells, and (ii) intracellular Ca2+-dependent signaling processes may be affected acutely by physiological concentrations of vitamin D3 metabolites.
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PMID:Vitamin D3 metabolites modulate dihydropyridine-sensitive calcium currents in clonal rat osteosarcoma cells. 247 47

An experimental model in rats for comparison of bone repair under normal and pathological conditions is described. The low cost of rats and the simple surgical procedure used allow large-scale studies. Although clinical implications must be interpreted with care, our model may prove useful in the attempt to understand how various drugs and metabolic disorders may affect bone healing. We used porous fiber titanium implants to replace a segment of the right proximal tibia in rats. The void space to be filled with bone represented a known and constant volume allowing a direct comparison between differently treated groups. Selected parameters for bone ingrowth could be expressed in terms of growth curves as a function of time, using a mathematical equation for restricted growth. The following parameters for quantity and quality of the ingrown bone were monitored: micromoles calcium as parameter for amount; calcium/hydroxyproline molar ratio for extent of mineralization; calcium/phosphorus molar ratio for maturity of minerals; and ultimate bending stress for strength of the bone-implant interface. With this model we have studied the effect that cis-platinum, an anticancer drug that is used in the treatment of osteogenic sarcoma, has on bone repair.
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PMID:Weight-bearing porous fiber titanium implants in rat tibia: a restricted growth model for comparison of normal and pathological bone repair. 248 9

Measurements of free cystolic Ca2+ ([Ca2+]i) and Ba2+ ([Ba2+]i) concentrations with Fura 2 were used to identify and characterize the properties of a depolarization-activated Ca2+ and Ba2+ entry in the plasma membrane of osteoblast-like cells. The presence of this pathway was demonstrated in two osteoblastic cell lines, UMR-106 and MC3T3-E1 and osteoblasts isolated from rat long bone and rat neonatal calvariae. Subsequent characterization of the pathway was performed in the osteosarcoma cell line UMR-106. Depolarization of the cells with high medium K+ was followed by an increase in [Ca2+]i which was dependent on medium Ca2+. Ba2+ ions depolarized the cells and were transported by this pathway. Mg2+ ions interfered with Ca2+ and Ba2+ entry. At 140 mM KCl and 1 mM MgCl2, the pathway could be saturated with Ca2+ or Ba2+. The apparent affinity for Ca2+ was 0.78 mM and for Ba2+ 1.82 mM. Ca2+ or Ba2+ entry into the cells was blocked by low concentrations of nicardipine, diltiazem, verapamil, and La3+. In the absence of an increase in [Ca2+]i or [Ba2+]i, the pathway inactivated within about 5 min after depolarization. When [Ca2+]i or [Ba2+]i was allowed to increase, the pathway inactivated within about 20 s. These properties suggest that Ca2+ and Ba2+ entry are mediated by an L-type, depolarization-activated Ca2+ channel in osteoblasts. The activity of these channels changes little with an increase or decrease in cell volume. Thus, it is concluded that these pathways do not provide the Ca2+ entry pathway required for initiation of volume decrease by osteoblasts.
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PMID:Properties of the depolarization-activated calcium and barium entry in osteoblast-like cells. 249 47

PTH-related protein (PTHrP), similarly to PTH, stimulates cAMP production in target tissues. However, different potencies have been observed for the two peptides in some biological assays, suggesting that cAMP-independent second messenger pathways might be involved in PTHrP signal transduction. This hypothesis was tested in the osteogenic sarcoma cell line UMR 106-01. Addition of PTHrP-(1-34) to cell suspensions loaded with the Ca2+ indicator indo-1 produced a transient dose-dependent increase in intracellular calcium ([Ca2+]i), with a maximal effect at 2 x 10(-7) M and an ED0.5 at about 4 x 10(-8) M. The amplitude and duration of the transients were similar to those induced by equimolar concentrations of bovine PTH-(1-34) (bPTH), and the dose-responses of the two peptides completely overlapped. Both full-length peptides, PTHrP-(1-141) and bPTH-(1-84), produced effects identical to those observed with the 1-34 fragments. Homologous and heterologous desensitization to both PTHrP-(1-34) and PTHrP-(1-141) occurred when the cells were prestimulated with equimolar or 10-fold lower doses of either PTHrP-(1-34) or bPTH-(1-34). Desensitization to bPTH-(1-34) was also observed when cells were prestimulated with PTHrP-(1-34). Furthermore, pretreatment with either bPTH-(3-34) or [Nle8,18, Tyr34]bPTH-(3-34) amide did not affect [Ca2+]i, but reduced the response to PTHrP-(1-34) by 55 +/- 10% (n = 3) and 67 +/- 8% (n = 3), respectively. The PTHrP-(1-34)-induced [Ca2+]i transient was not substantially affected by either extracellular Ca2+ chelation by EGTA or pretreatment with diltiazem, and nitrendipine only partially inhibited the [Ca2+]i response to PTHrP-(1-34) by about 10%. These results indicate that in osteoblastic cells PTHrP mobilizes Ca2+ from an intracellular storage pool with potency equal to that of PTH, and that the two hormones interact with the same receptor.
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PMID:Parathyroid hormone-related peptide transiently increases cytosolic calcium in osteoblast-like cells: comparison with parathyroid hormone. 250 65

In conclusion, we have cloned a full-length cDNA for human leukocyte 5-LO from differentiating HL-60 cells. The complete amino acid sequence of 5-LO has been determined from the nucleotide sequence of the cDNA. Some interesting features of the sequence include potential lipid and Ca2+ binding sites and sequence homologies with other lipoxygenases. Human osteosarcoma cells transfected with the 5-LO cDNA expressed 5-LO and LTA4 synthase activities that were indistinguishable from those of the human leukocyte enzyme confirming that the cloned cDNA was the correct gene.
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PMID:Cloning and expression of human leukocyte 5-lipoxygenase. 252 21

PTH-like proteins (PTHLP), which are associated with humoral hypercalcemia of malignancy, have recently been purified. Isolation of their corresponding cDNAs has revealed that they are derived from a single gene. In this report a synthetic gene encoding PTHLP-(1-141), a 141-amino acid protein corresponding to the most abundant PTHLP cDNA detected in human tumors, was expressed in bacteria and purified to homogeneity. Recombinant (r) PTHLP-(1-141) migrates with an aberrantly high mol wt on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, presumably as a result of its unusually basic pI. rPTHLP-(1-141), like PTH, induced hypercalcemia in rats, caused release of 45Ca from fetal rat bones, and stimulated the synthesis of cAMP by rat osteosarcoma cells and canine renal membrane preparations. A comparison of the abilities of rPTHLP-(1-141) and bovine PTH-(1-34) to stimulate cAMP synthesis indicated rPTHLP-(1-141) to be 5-fold more potent in the osteosarcoma assay, while nearly 30-fold less active in the renal membrane adenylate cyclase assay. Although 100-fold less potent than bovine PTH-(1-34) in promoting bone resorption, rPTHLP-(1-141) was a potent calcemic factor in vivo, inducing a rise in serum calcium from 10.4 to 14.5 mg/dl when infused into rats at 1.3 micrograms/h. These results support previous assumptions that PTHLP is the humoral factor responsible for humoral hypercalcemia of malignancy. In addition, they suggest substantial differences between PTHLP and PTH in the regulation of calcium homeostasis.
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PMID:Synthesis of a gene encoding parathyroid hormone-like protein-(1-141): purification and biological characterization of the expressed protein. 253 1

Our previous work demonstrated that the inhibition of type I collagen synthesis by 1,25-dihydroxyvitamin D (1,25-(OH)2D3) in fetal rat calvaria and cultured rat osteosarcoma cells is accompanied by equivalent reduction in steady state levels of alpha 1(I) and alpha 2(I) collagen mRNA. To pursue the mechanism for this effect, we isolated and sequenced a 3.6-kilobase DNA fragment that contained the promoter for the rat alpha 1(I) collagen gene. This promoter fragment was fused to the chloramphenicol acetyltransferase gene and was introduced into ROS 17/2.8 cells by calcium phosphate co-precipitation. Expression of this construct was diminished by 1,25-(OH)2D3 to the same degree as the endogenous collagen gene in both transient expression assays and in permanently selected bone cells. However, a fibroblast cell line did not show a similar reduction in the activity of the transgene or the endogenous collagen gene. These experiments indicate that the alpha 1(I) promoter contains cis-active elements which are regulated by the 1,25-(OH)2D3 receptor in ROS 17/2.8 cells.
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PMID:Isolation and characterization of the rat alpha 1(I) collagen promoter. Regulation by 1,25-dihydroxyvitamin D. 820 63

PTH binds to specific receptors that are coupled to adenylate cyclase and activate cAMP-dependent protein kinase. Since it has been shown that PTH activates phospholipid inositol metabolism, we investigated whether PTH influences protein kinase-C (PKC) activity in rat osteosarcoma (ROS) cells 17/2.8 that contain a large number of PTH receptor. Incubation of ROS cells with PTH or phorbol 12-myristate 13-acetate (PMA) for 1-30 min caused a rapid and transient decrease in PKC activity in the cytosol, which was associated with a transient increase in PKC activity in the membrane fraction. After 1, 5, 15, and 30 min of incubation with PTH, cytosolic PKC activity decreased to 57%, 74%, 84%, and 93% of the control value, whereas membrane PKC activity increased to 156%, 122%, 111%, and 106% of the control value, respectively. After PMA treatment for 1, 5, 15, and 30 min, cytosolic PKC activity decreased by 81%, 74%, 63%, and 44%, whereas membrane-bound PKC activity increased by 83%, 44%, 28%, and 17%, respectively. The effects of PTH and PMA on PKC were dose dependent, with ED50 values of 0.3 nM PTH and 4 nM PMA. Chronic treatment of ROS cells for 3 days with PMA caused depletion of total PKC activity in cytosolic and membrane fractions to less than 10% of that in control cells. Conversely, chronic treatment of ROS cells with PTH did not deplete PKC. In addition, chronic treatment of ROS cells with PTH inhibited the responsiveness of PKC activity to subsequent acute PTH challenge, but not to acute PMA challenge, suggesting specific desensitization of this response by PTH. Activation of cytosolic PKC by diolein, phosphatidylserine, and calcium caused phosphorylation of many cytosolic proteins, including those having apparent mol wt of 39K, 35K, 33K, 25K, 19K, and 16K. Pretreatment of ROS cells with PTH resulted in a transient decrease in the phosphorylation of these cytosolic proteins by PKC. This decrease in cytosolic protein phosphorylation by treatment with PTH is temporally associated with PTH-stimulated translocation of PKC activity from the cytosol to the membranes. These data suggest a potential role for PKC in the mechanism of action of PTH in ROS cells.
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PMID:Parathyroid hormone causes translocation of protein kinase-C from cytosol to membranes in rat osteosarcoma cells. 253 72


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